Sound recording apparatus



Jufiy 23, 1940. K. SCHWARZ SOUND RECORDING APPARATUS Filed April 30,1937 suarrse B A/71.15

Patented July 23, 1940 UNITED STATES SOUND maooamne APPARATUS KarlSchwarz, Berlin, Germany, assignor to Klangfilm G.,M. B. H., Berlin,Germany, a corporation of Germany Application April 30, 1937, Serial No.139,850 In Germany September 2, 1936 7 Claims.

This invention relates to sound recording apparatus, and moreparticularly to apparatus for recording sound photographically on astrip of film or the like.

More specifically, an apparatus is provided which adjusts the shape ofthe light beam used in variable density recording so as to vary thesensitivity of the apparatus in a predetermined manner, and to therebysecure either volume expansion or volume compression. volume expansionand volume compression are often referred to as dynamic regulation.

Sound recording with volume compression is well known in the art. Forexample, in accordance with Hanna Patent 1,888,724, a part of the soundcurrent is rectified, and this rectified part, which corresponds to theamplitude or envelope of the sound impulses, is employed for the purposeof controlling the degree of amplification of the recording amplifier sothat the soft sounds are recorded with a larger degree of amplificationthan the loud sounds, thereby securing volume compression.

In the present invention, a particularly simple process of volumecompression is provided, which is distinguished by the fact that it doesnot operate on the recording amplifier, and nothing in the electricalpart of the recording apparatus is afiected. Thus the control in thiscase is effected mechanico-optically, and this is done in such a mannerthat the angle of intersection of the light beam with the optical slitchanges according to the amplitude of the sounds. This change of angleis accomplished by means of movable diaphragms, and may be applied bothto variable area and variable density films.

In recording variable area films, a rotatable straight edged diaphragmis moved about an axis parallel with the optical axis of the apparatus,so that at small amplitudes the angle of intersection of the light beamwith the slit is small, and at larger amplitudes it is large.

In recording variable density sound records, the diaphragm may be soarranged as to produce a partially shaded area over the recording slit,in the same manner as is done in what is commonly referred to aspenumbra recording; or a variable density wedge may be utilized forcontrolling the light intensity in accordance with the sound amplitude.

In recording variable area film, I prefer to use a recording system suchas that shown and described in Dimmick Patent 1,999,721, wherein arecording galvanometer vibrates about a hori- The terms according to theinvention are shown in the illustrations. In Fig. 4, the principle ofthe invention is illustrated by means of difierently steep lightcharacteristic lines. light controlling organ is indicated on theabscissa .A, and the amount oflight transmitted through 55 ticallyacross the recording slit. In such an apparatus, however, instead ofusing a triangular aperture of fixed shape, I use a pair of movablediaphragms to define the sides of the triangle, and move thesediaphragms angularly in accord- 2:5 ance with the amplitude of the soundinorder to secure volume compression.

'I'his portion of. the apparatus may be designed in such a way that allsounds are recorded with the same or nearly the same amplitude, or the10 characteristics of the apparatus may be so chosen as tozsecure anydesired degree of volume compression.

One object of my invention is to provide a novel method of volumecompression or expansion. 15

Another object of my invention is to provide a novel apparatus forvolume compression or expans1on..

Another object of my invention is to provide a novel apparatus forsecuring ground noise re- 20 duction.

Another object of my invention is to provide a novel means forcontrolling the shape of a recording light beam.

Other and incidental objects of my invention .25 will be apparenttothose skilled in the art from a reading of the following specificationand an inspection of the accompanying drawing, in which Figure 1 is anillustration of a triangular light spot as it appears upon the slit ofan optical system in unilateral recording,

Figure 2 is an elevation of one form of the invention, showing therelation of the movable shutters to the recording slit as projected onthe shutters, i

Figure 3 is a diagrammatic illustration of the application of oneshutter according to my invenpression.

For the purpose of illustrating and explaining the invention in detail afew styles of execution The angular rotation of the the slot isindicated on the ordinate L. There are shown two light characteristiclines, having a different steepness, with I and II. When amplitude m iscontrolled outward on characteristic line I, a recorded amplitude at isobtained between the two limiting lines I and II. In case the sameamplitude as is controlled outward on the other characteristic line II,there results a recorded amplitude 33" between the dotted lines II. Thisamplitude is smaller than amplitude at. If it is, therefore, intended toobtain a recording with dynamic compensation in such a manner that thesounds are previously recorded with a constant amplitude, one proceedsso as to change the steepness of the light characteristic line in such away that there exists a small steepness (characteristic line II) withlarge amplitudes and a large steep ness (characteristic line I) withsmall amplitudes In Fig. 1 is illustrated how the idea illustrated inFig. 4 may be utilized. The slot is indicated at t and the edge of thediaphragm on the slot is indicated at 2. When the angle at between slot1 and the diaphragm edge 2 is changed in such a way that the image ofthe diaphragm edge 2 is displaced in the direction of the double arrow,the steepness of the light characteristic line experiences a change bythis fact. If the angle or is small, there is a large steepness. Incasethe angle a is large, there is a small steepness of the characteristicline.

In order to make a record with an arrangement according to Fig. 1, oneproceeds, for instance, in such a way that diaphragm 2 is portrayed onthe slot over a swinging mirror, and that the turning of the diaphragmedge 2 in relation to slot i is obtained by turning the diaphragmaccording to the volume or envelope of the sound currents. In Fig. 2there is shown another style of execution, viz. for recording adouble-hump record. The slot is again indicated at I, and the diaphragmedge at 2. In principle, there is no difference between illustration 2and illustration 1. The recording takes place in the same manner; onlythe style of execution of the diaphragm and its drive is different aswill now be explained. The diaphragm consists of two circular sectors,3, turning around the pivot 'or axis 4. There are two lever arms 5 and 6pivoted to these two diaphragm sectors by pins 1 and 8. The ends oflevers 5 and 8 are pivoted to a common pin 9. This pin rests in a guidewhich is designed as a straight guide. By a dynamic or magnetic system,acting on this straight guide, it is possible to eiiect the control ofthe diaphragm according to the volume of the sound as will become moreapparent upon consideration of Fig. 5.

On the basis of Fig. 3, it will be shown schematically that in recordingvariable density films one can proceed according to the same principleof the invention. A light source is indicated at It, and a diaphragmedge at I or II. When light source I is allowed to illuminate the areaa-a over diaphragm edge I, there is obtained a light characteristicline, as it is shown with I in Fig. 3d. When the diaphragm edge isturned from position I into position II, a light distribution accordingto characteristic line 11 is obtained. According to the invention, thisdiaphragm edge is allowed swinging with the light distribution indicatedby the characteristic line over aswinging mirror and over a slot. As thesteepness of the light characteristic line can be changed, as statedabove, the recording takes place in principle exactly like that whichhas been described in con- 75 nection with amplitude or variable arearecording. This will be recognized as penumbra recording such as thatdisclosed by Dimmick Patent 2,095,317. Instead of employing a planarlight source and a diaphragm edge, one can also use a blurredlyportrayed diaphragm edge or a gray wedge, as this is well known in soundfilm technics. If these well-known arrangements are employed forapplying the idea of the invention, they will also come under theinvention.

The optical system shown in Fig. illustrates the practical applicationof this invention to an optical system such as shown in the Dimmickpatent above referred to. In this arrangement, the exciter lamp l0passes light through the lens H to the aperture l2 which is constructedin the manner shown in Fig. 2, the reference characters being the sameon corresponding parts, and an additional stop l3 being added to definethe upper edge of the triangular beam. The magnetic means l4 foractuating the shutters in accordance with the volume of the sound isalso shown. The lens l5 directs the light on the galvanometer mirror 16where the beam is vibrated in accordance with the sound waves to berecorded and from which it is reflected through the lens I! to theaperture plate [8. An objective lens l9 focuses the image of the line oflight passing through the plate l8 upon the film 20.

In the further modification of the invention shown in Fig. 6, themovable shutters 2 are pivoted at their outer ends and the links 5 and 6are connected to them at their adjacent ends. In this case the positionof the image of the light slit is indicated at i and it will be apparentthat movement of the shutters 2 instead of merely changing the shape ofthe triangular aperture also changes the position thereof, as indicatedat 2. By means of this arrangement, not only can the sensitivity of theapparatus be varied in accordance with the volume, as is the case inFigs. 2 and 5, but ground noise reduction may also be accomplished in amanner similar to that described in the aforesaid Dimmick patent. Forexample, at low amplitudes the magnet I4 will not be energized and theshutters will be in the position 2' giving it a high sensitivity and atthe same time providing a very narrow track width producing very littleground noise. As the amplitude of the sounds is increased, the magnet I4 is correspondingly energized and moves the shutters 2 downwardly tothe position shown where the average exposure covers approximatelyonehalf of the track width and where the sensitivity is correspondinglyless due to the changed shape of the triangular beam of light.

Having now described my invention, I claim:

1. Apparatus of the class described, including means providing a li htslit, means for projecting on said slit an image of a light aperturehaving a straight edge, means for moving said image in accordance withsounds to be recorded, and means for changing the angular relationbetween said edge and said slit in accordance with the amplitude of thesounds to be recorded.

2. Apparatus of the class described, comprising a pair of shuttersmovable to define the shape of a light beam, and means for moving saidshutters in accordance with only the average amplitude of the sounds tobe recorded.

3. Apparatus of the class described, including means for projecting animage of a light aperture upon a slit, means for moving said image inaccordance with sounds to be recorded, and

means for varying the angular relation between 15 the sides of saidimage in accordance with the amplitude of the sounds to be recorded.

l. Apparatus of the class described, comprising means for projecting atriangular beam of light upon a narrow slit, and means for changing theangular relation between the sides of said image in accordance with onlythe average amplitude of the sounds to be recorded.

5. Apparatus of the class described, comprising a pair of shuttershaving cooperative straight edges movable to define the shape of a lightbeam, and means for changing the angular relation between said edges inaccordance with only the average amplitude of the sounds to be recorded.

6. Apparatus of the class described, comprising a pair of shutterspivoted at their adjacent ends and movable to define the shape of alight beam, and means for moving said shutters in accordance with onlythe average amplitude of the sounds to be recorded.

7. Apparatus of the class described, comprising a pair of shutterspivoted to rotate about their non-adjacent ends and movable to definethe shape of a light beam, and means for moving said shutter inaccordance with only the average amplitude of the sounds to be recorded.

KARL SCHWARZ.

